@Paul ****
, okay, first off we need to know what office you got your yearly extension at..
AFAIK, at this time ONLY the immigration office in Jomtien is handing out a paper that has a date 3 months after your extension application which says to update your bank book and take it in to show them on that date so they can make sure the 800K is still in the account.
If you didn't get a paper like that I would say your immigration office doesn't require it (Bangkok, Chiang Mai, etc don't).
And no, your 90 day reporting has nothing at all to do with this requirement at the immigration offices that have you come back.
If you're going to be out of the country on that 3 month date you're supposed to report back on you go as soon as you get back.